Hey frenzi,

They sound about the right height for their age considering you've topped them, it's good to have them short and stocky you don't want lanky plants.

Most growers will tell you to wait until the plant is sexually mature before switching to 12/12 as flowering earlier can reduce yield and potency. A sign of maturity is when the plant produces alternating nodes (the leaves don't grow out of the stem side by side but with a gap between them "alternating")

Good luck!